See, that's what I thought about myself and my needs, too, when I got a 6s Plus, so I got a 128GB model. It was almost completely full for the majority of the past two years. But then I thought about it and realized that over the past two years, while I might want to listen to deep cuts from my collection every now and then, I almost never want to listen to them when I'm using my phone. I want to listen to those songs on a stereo. The songs and albums that I typically listen to on my phone? Those hardly take up any space.
So for my next phone, I'll totally be set with 64GB. I'll still have plenty of space after downloading music from the Google servers and pinning it to my phone.